Several synthetic routes to these compounds are well known at present. In particular, there are known reactions which involve a methacrylic acid, or its esters, and an amine. This type of reaction has the severe disadvantage of competing with a secondary reaction: this is the Michael reaction, that is to say the addition of the amine to the (meth)acrylic double bond. For this reason, the various processes for the synthesis of an N-dialkylaminoalkyl(meth)acrylamide are complex processes consisting of several reaction steps.
Thus, the process described in U.S. Pat. No. 3,878,247 and Canadian Pat. No. 1,020,163 involves reacting a diamine of formula (R.sub.2)(R.sub.3)N--(CH.sub.2).sub.n --NH.sub.2 (where R.sub.2 and R.sub.3 are, in particular, alkyl groups) with an acid or an ester of the formula H.sub.2 C.dbd.CR.sub.1 --COOZ (where R.sub.1 is a methyl radical or a hyrogen atom, and Z is a hydrogen atom or an alkyl group). This reaction gives an intermediate product, resulting from the amidification of the acid group or of the ester group of the (meth)acrylic derivative, and from the Michael addition of the diamine to the methacrylic double bond. This is the .beta.-aminopropionamide of formula: EQU (R.sub.2)(R.sub.3)N--(CH.sub.2).sub.n --NH--CH.sub.2 --CH(R.sub.1)--CO--NH--(CH.sub.2).sub.n --N(R.sub.2)(R.sub.3)
The thermal decomposition of this intermediate product at 210.degree.-250.degree. C., in the presence of a catalyst (U.S. 3,878,247), or without a catalyst but at 180.degree.-300.degree. C. (CA. 1,020,163), yields the N-dialkylaminoalkyl(meth)acrylamide.
There are also known processes for the synthesis of an N-dialkylaminoalkyl(meth)acrylamide in which the Michael reaction is avoided.
According to a first such process, which is described, in particular, in German Patent No. 2,856,383 and in European Patent No. 13,416, an amide of a .beta.-hydroxycarboxylic acid is reacted with an amine and the intermediate product is then dehydrated at a temperature of between 200.degree. and 400.degree. C., ultimately to yield the desied (meth)acrylamide.
Another process involves using a catalyst which inhibits the Michael reaction of the amine with the double bond of the (meth)acrylic ester. The recommended catalysts in a reaction of this type are, in particular, organostannous compounds in U.S. Pat. No. 4,321,411, dialkyltin oxides in German Pat. No. 2,816,516, or alternatively alkyl titanates in German Pat. No. 3,048,020. The use of this process requires precautions so as not to poison the catalyst.